1. Field of the Invention
This invention relates to vent, exhaust stack or chimney structures and, more particularly, to a device for stabilizing the draft in a stack or chimney against varying wind conditions at the exit end of the stack or chimney.
2. Description of the Prior Art
As energy costs have increased, it has been recognized that one method of conserving energy is to avoid losses occurring by movement of air or energy through the walls, ceilings or other boundaries of enclosed structures. This recognition has led to increased interest in insulation, and to weather-tight closures for doors, windows and chimneys. It has also been recognized that combustion systems used to heat enclosed structures can be improved in various ways to reduce energy consumption. This has resulted in new burner or control system designs, damper arrangements and other improvements.
Among the specific sources of energy loss which have been recognized is the loss occurring through vent or exhaust stacks and chimneys. Such stacks are found in homes in connection with hot water heaters or furnace vents, as well as with fireplaces. Such stacks also are found in larger residential or commercial buildings and also in some vehicles. In connection with such stacks it has been recognized that ambient wind conditions influence the flow of air or exhaust gases from such stacks; some remedial devices have been proposed. (See, e.g., U.S. Pat. Nos. 2,701,999; 2,711,683; 2,818,060; 3,040,734; 3,315,586; 3,361,051.) Most stack paths and their attached equipment are designed to have proper draft flow primarily in still air conditions. Such conditions obviously do not always prevail. With most stacks, a strong wind current across the exit end will cause a vacuum and an updraft, pulling more air or exhaust gas up the stack than under normal draft conditions. In winter, the air which is pulled up the stack from an inhabited structure is heated and, frequently, humidified. Loss of such air will necessarily cause a loss of energy and may also cause discomfort. In pulling out the warmed and humidified air, an updraft may also cause cold, outside air to be pulled into the building through cracks or other leaks.
In addition to robbing an inhabited space of warm, humidified air, during the burning or "on" phase of a combustion system a wind-induced updraft may also cause abnormal combustion conditions by pulling excess air into the burner on some types of furnaces. The effect of this will be to disturb the air-fuel ratio and decrease combustion efficiency.
The problems caused by wind-induced updrafts are not limited to cold seasons. In summer, an updraft may suck cooled, possible dehumidified, air up a stack and draw warm, moist air in through cracks or other openings. Even in buildings without air conditioning, an updraft may cause problems by pulling cool basement air up through a furnace draft hood or other opening.
It will be observed that the problems caused by wind-induced updrafts occur in both warm and cold seasons. In addition, they may occur during both the "on" and "off" phases of the combustion system which is served by the stack.
While crosswinds generally cause updrafts, certain other wind conditions may cause downdrafts in a stack. Although it is less likely to involve loss of heated or cooled air, a downdraft may, nonetheless, disturb combustion efficiency or drive exhaust gases into inhabited space. In extreme cases it may even extinguish combustion. Accordingly, a stack should be protected against downdrafts as well as updrafts.
A primary prior solution to the updraft and downdraft problem in stacks is use of a stack damper. A damper may be installed at various points in a draft flow path and be actuated by temperature or other parameters so as to be open for the burning or "on" phase and closed when no burning is occurring. (See, e.g., U.S. Pat. Nos. 4,017,024; 4,020,754.) Such a damper can obviously be of benefit in controlling draft flow during the non-burning phase, but it may do little or nothing to prevent updrafts or downdrafts during the burning cycle. Another disadvantage of a damper is that it generally involves moving parts and sensors which may fail to operate properly under the often harsh conditions of an exhaust stack.